The purpose of this project is threefold: 1) to identify "addict" smokers, viz., those smokers who experience withdrawal from nicotine per se; 2) to identify experimentally the nature, course and duration of withdrawal symptoms and to isolate those symptoms induced specifically by the removal of nicotine from those induced by removal of secondary reinforcers; and 3) to experimentally determine the effectiveness of nicotine gum (nicotine replacement) in producing successful cessation in those smokers for whom behavioral and self-control techniques are inadequate. Four studies have been designed with these objectives in mind. The first will look at the appearance and course of withdrawal symptoms in a systematic exploration of "cold turkey" cessation in males and females. The study also represents the beginning of testing of a questionnaire designed to identify "addict" smokers. Throughout all the studies, this instrument will be refined and used in subject selection. The second study will test for nicotine-specific withdrawal symptoms by comparing the appearance and alleviation of such symptoms with nicotine vs. placebo gum. It simultaneously will test the efficacy of a replacement-extinction cessation procedure in nicotine-seeking smokers. The third study represents an attempt to determine whether self-imposed replacement schedules are superior or inferior to experimenter-controlled techniques. The fourth study will subject the derived selection techniques to test by comparing these techniques to random selection in the final manipulation of nicotine vs. placebo gum. In all studies, physiological as well as psychological measures of withdrawal aze taken. Intense follow-up of cessation will continue for one month and long-term follow-up on a monthly basis will continue for one year. Information obtained in all studies will be used to determine "causes" recidivism as well as to understand the nature of withdrawal and the relationship between certain smoker characteristics and successful cessation. In sum, the intent of the investigation is to examine the efficacy of nicotine gum as a valid and reliable experimental and clinical tool in the study of smoking and smoking cessation.